A protection plug of the type referred to hereinbefore is described in DE 40 26 004 C2. This plug is adapted as a stage protection with a measuring and disconnecting position. The protection plug comprises a housing, the lower side of which is formed by a printed-circuit board, a voltage-surge suppressor, a slider, a spring, an earth plate, a signalling lug, a solder position melting with an inadmissible heating-up of the voltage-surge suppressor and causing a movement of the slider, which in turn will move the signalling lug outwardly for indication.
Disadvantageous, in this prior art protection plug, are the large number of individual parts used, thus an economical manufacture being difficult, and the load on the solder position exerted by the helical spring being tensioned, which may cause flow of the solder material.